Stuck Tranny

I have a 1996 Mits Mirage and the transmission is stuck in drive.
I can shift the mechanism, and start the car. The car moves ahead in neutral and drives normal in drive. The engine starts under load.
The fluid was recently changed and it had been acting up. There is no reverse. I am trying to sell the car. I appreciate any input.

Thanks
John

if its automatic, has the shifter knob been takin off?, if so it matters how much the knob is screwed on before the screws are put in. and check to see if the shifter cable is free and not bound, or stuck like under the battery.